The present invention relates generally to an automatic transmission of a motor vehicle that allows manual shift and more particularly, to a manual shift control system for use therein.
With the automatic transmission that allows manual shift, if shifting to a speed ratio corresponding to a manual shift command is carried out without taking account of the vehicle cruising state, the following problem arises. When providing a manual shift command to a low speed ratio at high vehicle speed, the engine falls in over-rotation, whereas, when providing a manual shift command to a high speed ratio at low vehicle speed, engine vibrations are transmitted to a vehicle body.
Generally, as disclosed, for example, in JP-A 7-83327, a shift pattern for each speed ratio corresponding to a manual shift command is determined with the operation area wherein selection of a corresponding speed ratio is not allowed. In this operation area, automatic shift is carried out instead of manual shift so as not to produce the above problem.
With the known structure, however, since a upshift or downshift manual shift command is accepted even during execution of automatic shift in the manual range, manual shift corresponding thereto is carried out besides automatic shift, causing the following problem:
By way of example, if automatic shift in the manual range aims to prevent over-rotation at high vehicle speed, it naturally concerns upshift transmission for decreasing the engine speed. When a driver, who does not know this automatic shift, wants shifting to one-stage higher speed, he carries out an operation to provide a upshift manual shift command. At that time, the known structure ensures shifting of upshift transmission due to automatic shift plus upshift transmission corresponding to a upshift manual shift command. As a result, though the driver wants shifting to one-stage higher speed, shifting to two-stage higher speed is carried out. The driver has to then carry out an operation to provide a downshift manual shift command, resulting in a troublesome operation.
The foregoing is an inconvenience in the operation area wherein selection of a corresponding speed ratio is not allowed in the manual range. With the known structure, even in the operation area wherein selection of a corresponding speed ratio should be allowed, the following problem arises when upshift manual shift commands are provided consecutively:
If upshift manual shift commands are provided consecutively, the automatic transmission cannot ensure shifting to a final speed ratio through sequential progress of speed ratios corresponding thereto due to a shift response lag, but substantially so-called jump shifting that a current speed ratio abruptly proceeds to a final speed ratio. This jump shifting accompanies a great variation in the engine speed, so that friction elements such as clutch put in engagement upon shifting should absorb corresponding rotational energy, increasing the heat amount of the friction elements, causing overheat thereof. This inconvenience is remarkable as the vehicle speed is higher.
It is, therefore, an object of the present invention to provide a manual shift control system for use in automatic transmissions, which is free from the above problems, and enables easy and excellent manual shift.